Elementary Photographic Chemistry PDF Download

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1921 edition. Excerpt: ...no water of crystallization. One part, by weight, of the fused sulphide is equivalent to three parts, by weight, (approx.), of the crystals. Sodium sulphide often contains impurities, chiefly iron, though by dissolving in hot water the iron sulphide quickly separates out as a black sludge, leaving a clear solution which should be decanted. Old sodium sulphide often contains hypo, since hypo is produced in the oxidation of sulphide, and if hypo is present in any considerable amount, some of the silver bromide will be dissolved by it and the print will lose strength in the highlights and give a very inferior result. All sulphides give off a certain amount of hydrogen sulphide, which smells offensively, and which is extremely dangerous to photographic materials, since a very small amount of hydrogen sulphide will convert enough of the silver sulphide or chloride of the material into sulphide to produce a severe fog. No photographic materials should therefore be stored in a room where sulphides are kept or where sulphide toning is done. It has already been explained that the color of silver sulphide depends upon its state of division, and since the state of division of the toned image depends upon that of the untoned image and this again upon the treatment of the material, it is evident that the exposure and development of the print will have an effect upon the result obtained. As a general rule, it may be stated that to get good colors in sulphide toning it is necessary that a print should have been fully developed and not over-exposed; a print which is very fully exposed and then developed for a short time will not give a good tone. CHAPTER VI. The Chemistry of Reduction and Intensification REDUCTION. By reduction in photography is meant...